Vol. 70.] GLACIAL G-EOLOUY OF EAST LANCASHIRE. 209 



on the map (PL XXXIII) by arrows marking the direction o£ the 

 scratches. Their number, is, however, disappointingly small, owing 

 to the fact that, where good striae might be expected, the surface 

 of the rock is often rubbly and broken into fragments, or the 

 Drift-cover has been too thin to protect the rock-surface from 

 subsequent denudation by atmospheric agencies. Moreover, the 

 area does not appear to have been subjected to vigorous 

 giaciation. 1 



There are numerous examples of ' terminal curvature ' due to the 

 ploughing action 3 which goes on at the base of an ice-sheet. In the 

 preparation of a list 3 of especially good instances of this pheno- 

 menon, care has been taken to eliminate sources of error, due to the 

 possible effects of landslip and soil-creep, by recording examples in 

 which the disturbing influence has clearly acted up hill. It is also 

 noteworthy that, although these examples yield no such exact record 

 of the direction of ice-movement as can be obtained from clear 

 scratches on undisturbed rock, their evidence is never in opposition 

 to the rest of the evidence from which the directions of ice- 

 movement are inferred, and is therefore of great positive value in 

 supporting the latter. 



In close relationship with the evidence derived from striae and 

 terminal curvature, is the uplift of boulders of local rocks. Most 

 of the hills making up the Eossendale highland are capped by 

 Coal-Measure rocks. Millstone Grit cropping out at lower levels 

 on the hillsides. The occurrence of boulders of Millstone Grit 

 on high ground consisting of Coal-Measure rocks is therefore good 

 evidence of uplift by the distributing agent, in some cases to the 

 extent of at least 200 feet. 



Further evidence of the existence of an ice-sheet is furnished by 

 the succession of valleys, trenching the hillsides parallel with the 

 contours and cutting across spur after spur, which can only be 

 satisfactorily explained by reference to a fluctuating barrier such 

 as an ice-sheet would provide. 



IV. Inferences respecting the Ice-Sheet 



AND ITS Mote ME NTS. 



The evidence already examined points to the general conclusion 

 that East Lancashire was invaded by two streams of ice, one 

 from Kibblesdale flowing southwards between Pendle and Bonis- 

 worth Hills, and a much larger stream flowing south-eastwards, 

 passing over the western part of the Eossendale highland, 

 inundating the plain on the south of this ridge, and reaching high 

 up the western slopes of the Pennines at Blackstone Edge. The 

 fusion of these tAvo streams into a great ice-sheet in North 



1 See p. 210. 



2 R. H. Tiddeman, Q. J. G. S. vol. xxviii (1872) pp. 482-83 : and J. Eccles, 

 'Superficial Curvature of Inclined Strata near Blackburn' Trans. Manch. 

 Geol. Soc. vol. vii (1867-68) p. 20. 



3 See Appendix, p. 227, and the broken arrows on the map (PI. XXXIII). 



